#include <bits/stdc++.h>
using namespace std;

ifstream f("lupu.in");
ofstream g("lupu.out");

priority_queue <int> Q;

struct nod
{
    int x, y;
}v[100001];

bool cmp(nod i, nod j)
{
    return i.x < j.x;
}

int n, d, k, i, lim, val;
long long s;

int main()
{
    f >> n >> d >> k;

    for(i = 1; i <= n; ++ i)
        f >> v[i].x >> v[i].y;

    sort(v + 1, v + n + 1, cmp);

    i = 1;
    while(lim <= d && i <= n)
    {
        while(i <= n && v[i].x <= lim)
        {
            Q.push(v[i].y);
            i ++;
        }

        if(!Q.empty())
        {
            val = Q.top();
            s = s + val;
            Q.pop();
        }

        lim = lim + k;
    }

    g << s;

    f.close();
    g.close();

    return 0;
}